This invention relates to creation of electrical coronas, and in particular to an electrode arrangement and method of treating where electrically-conductive surfaces can be treated without arcing from the electrode to the surface.
As explained in U.S. Pat. No. 5,019,709, the disclosure of which is incorporated herein by reference, many materials, when molded, will not accept an adhesive, a coating, labels, inks or other printing vehicles unless the surface of the plastic has been chemically and/or physically altered. U.S. Pat. No. 5,019,709 discloses a particular electrode arrangement for creating a corona for treating surfaces for adherence of such vehicles. The electrode is activated by a high frequency electrical corona generator which is used to generate resonant frequencies on the order of 2 MHz and above. The BD-80 corona generator manufactured by Electro Technics Products, Inc., Chicago, Ill. USA, the assignee of the present application, is one such corona generator which functions quite adequately.
When a surface to be treated is electrically conductive, such as containing carbon or other conductive material, corona treating is difficult since the natural tendency is to extinguish the corona and, instead, create an arcing condition where the current arcs from the electrode directly to the item to be treated, without, therefore, actually treating that item. It is therefore desirable to create a corona treatment structure which can not only treat plastics, but also materials which are electrically-conductive.